Volume 11, Issue 2, Pages 175-182 (April 2015) IKCa Channels Are a Critical Determinant of the Slow AHP in CA1 Pyramidal Neurons  Brian King, Arsalan P. Rizwan, Hadhimulya Asmara, Norman C. Heath, Jordan D.T. Engbers, Steven Dykstra, Theodore M. Bartoletti, Shahid Hameed, Gerald W. Zamponi, Ray W. Turner  Cell Reports  Volume 11, Issue 2, Pages 175-182 (April 2015) DOI: 10.1016/j.celrep.2015.03.026 Copyright © 2015 The Authors Terms and Conditions

Cell Reports 2015 11, 175-182DOI: (10.1016/j.celrep.2015.03.026) Copyright © 2015 The Authors Terms and Conditions

Figure 1 TRAM-34-Sensitive Mechanisms Contribute to Spike Accommodation and the sAHP (A) Spike accommodation during depolarizing current injection is reduced by 1 μM TRAM-34 to increase spike number and frequency. Mean bar plots indicate the fold change in spike frequency or spike number over the times indicated by horizontal bars following TRAM-34. (B) Repetitive SR stimulation (30 pulses, 50 Hz) in the same cell as in (A) is associated with prominent EPSP suppression and spike accommodation that is reduced by infusion of 1 μM TRAM-34. Open arrows and inset illustrate the effects of TRAM-34 on the sAHP that follows a synaptic train. Mean bar plots indicate the fold change in spike frequency or spike number over the times indicated by horizontal bars following TRAM-34. (C) Repetitive SR stimulation (30 pulses, 50 Hz) at sub- or supra-threshold intensity in the absence of picrotoxin to preserve inhibitory inputs reveals a significant effect by TRAM-34 (1 μM) on EPSP summation and spike output. All recordings in (A) and (B) were obtained in 100 nM apamin, 10 μM XE-991, and 50 μM picrotoxin, while those in (C) did not include picrotoxin. In all cases, TRAM-34 was internally perfused through the electrode. Values are mean ± SEM; ∗p < 0.05. See also Figures S1–S3. Cell Reports 2015 11, 175-182DOI: (10.1016/j.celrep.2015.03.026) Copyright © 2015 The Authors Terms and Conditions

Figure 2 The sAHP Is Reduced in KCa3.1−/− Animals (A) Current-evoked firing in CA1 pyramidal cells of KCa3.1−/− mice lacks sensitivity to internal infusion of 1 μM TRAM-34. (B) Responses in mouse CA1 pyramidal cells to SR stimulus trains (30 pulses, 50 Hz) reveal an sAHP in WT, but not KCa3.1−/−, animals that is reduced by 1 μM TRAM-34 in WT animals. (C) Mean sAHP area in WT and KCa3.1−/− mice before and after TRAM-34 for tests as in (B). (D) Mean baseline membrane voltage normalized to the voltage at the start of repetitive SR stimulation (as in (B) reveal a suppression of EPSP summation in WT animals that is reduced to that of KCa3.1−/− animals by 1 μM TRAM-34. (E) The sAHP following five-pulse 50 Hz SR stimulus trains in rat pyramidal cells is reduced by the IKCa blocker Senicapoc (100 nM) and enhanced by the IKCa agonists DC-EBIO (0.1 μM) or SKA-31 (1 μM). (F) Superimposed recordings of five-pulse 50-Hz SR stimulus trains in pyramidal cells of KCa3.1−/− mice in control conditions and after sequential perfusion of DC-EBIO (0.1 μM) and SKA-31 (1 μM) show no effect on the afterpotential. All recordings were obtained in 100 nM apamin, 10 μM XE-991, and 50 μM picrotoxin. TRAM-34 was internally perfused through the electrode. Values are mean ± SEM; ∗p < 0.05, ∗∗p < 0.01, ns, not significant, paired Student’s t test (A), two-way ANOVA (C), and repeated-measures ANOVA (F). Cell Reports 2015 11, 175-182DOI: (10.1016/j.celrep.2015.03.026) Copyright © 2015 The Authors Terms and Conditions

Figure 3 CA1 Pyramidal Cells Exhibit an Outward Current with a Pharmacological Profile Consistent with IKCa Channels Shown are outside-out recordings from pyramidal cell somata with 1 μM [Ca]i in response to a 500-ms ramp command from −110 mV to +60 mV. Mean I-V plots reflect currents blocked by the indicated agents following subtraction of test from control recordings. IKCa current was isolated using blockers described in the Supplemental Experimental Procedures. (A–D) In each case, outward current is voltage independent and reduced by (A) TRAM-34 (1 μM), (B) ChTx (100 nM), (C) MTx (100 nM), or (D) PKAcat (100 U/ml). ChTx and MTx were focally pressure ejected, while TRAM-34 and PKAcat were internally perfused in the patch electrode. SEMs for mean values in I-V plots are indicated by the shaded area. Cell Reports 2015 11, 175-182DOI: (10.1016/j.celrep.2015.03.026) Copyright © 2015 The Authors Terms and Conditions

Figure 4 IKCa Channels Are Expressed in CA1 Pyramidal Cells Shown are on-cell somatic recordings using a HEPES-buffered aCSF internal solution, with Ca2+ influx evoked by a repetitive spike-like command (50 Hz, 20 pulses, 5 ms, 80 mV) followed by steps to different steady-state potentials. The resting membrane potential (RMP) across the patch is presumed to be approximately −65 mV for records in (A), (C), and (D) with 3.25 mM [K]o, while that for 140 mM [K]o in (B) was set at −65 mV. Voltage commands reflect the step applied to the electrode and displayed with net depolarizing commands upward. Current is displayed with respect to the cell interior with outward current as an upward deflection. The mean I-V plot in (B) reflects TRAM-34-sensitive currents calculated by subtraction of test from control records. (A) On-cell recording using 3.25 mM [K]o in the electrode reveals single channel activity following the pulse train that is rapidly reduced or blocked by 1 μM TRAM-34. Current reversed approximately −10 mV from the resting state. (B) On-cell recordings of macroscopic current using equimolar [K]o exhibits reversal of TRAM-34-sensitive current through 0 mV (EK). (C) On-cell recorded macroscopic current is enhanced by the IKCa agonist DC-EBIO (0.1 μM) and blocked by 10 mM BAPTA-AM. (D) On-cell macroscopic current is reduced by 100 μM 8-bromo-cyclic AMP. Records in (B) show every second record for clarity. The electrode and bath perfusate in all cases contained blockers as described in the Supplemental Experimental Procedures. Traces were filtered at 400–500 Hz (8-pole Bessel). Values are mean ± SEM. Cell Reports 2015 11, 175-182DOI: (10.1016/j.celrep.2015.03.026) Copyright © 2015 The Authors Terms and Conditions

Figure 5 IKCa Channels Are Evoked in CA1 Pyramidal Cells by Synaptic Stimulation (A and B) On-cell recordings with a HEPES-buffered aCSF electrode solution (3.25 mM [K]). Currents are illustrated with respect to the cell interior (outward current upward). Currents were evoked using a 50 Hz, five-pulse SR stimulus train with a net 60 mV depolarized holding potential to increase driving force for K+ across the patch. The electrode and bath perfusate contained blockers as described in the Supplemental Experimental Procedures. (A) A single channel is activated during and following a five-pulse SR stimulus train and is blocked by bath perfusion of 1 μM TRAM-34. Dashed lines depict open (o) and closed (c) states, with the same example expanded below. (B) On-cell recordings of an outward macroscopic current that opens for prolonged but variable periods of time following SR stimulus trains (arrows) and is reduced or blocked by TRAM-34. An ensemble average from 9 SR stimulus trains (lowest trace) reveals an average time course equivalent to an sAHP. Transients in (B) reflect capacitive transients from spontaneous spike discharge in the cell. (C and D) Comparison of outward current evoked by SR stimulation to the IsAHP evoked by a step command in perforated-patch recordings in the presence of 100 nM apamin, 10 μM XE-991, and 50 μM picrotoxin (C and D), with 5 mM TEA further included in (D) to block BK channels for tests with ChTx. Currents were evoked by five supra-threshold SR stimuli (50 Hz) or a 500-ms step to 60 mV to evoke IsAHP and bath apply 1 μM TRAM-34 or pressure eject 100 nM ChTx. Results in (C) and (D) are from separate cells. Traces in (A) and (B) were filtered at 500 Hz and the expanded trace in (A) at 1 kHz (8-pole Bessel). Values are mean ± SEM. Cell Reports 2015 11, 175-182DOI: (10.1016/j.celrep.2015.03.026) Copyright © 2015 The Authors Terms and Conditions